How Combing Hail Damaged AC Units Can Result in a 95% Drop in Costs Versus Replacement.

A major hailstorm hits and a shopping center with dozens or possibly hundreds of rooftop HVAC units is claiming that their AC units are damaged beyond repair.  Do all the units truly require replacement, or are there more cost effective measures to repair?  In many cases, the damaged condenser fins can be combed, restoring the units to pre-loss or better efficiency, without replacing any equipment. Keep reading for a breakdown of what combing is and how it can help reduce claimed costs. 

Why is Hail Damage a Problem?

The basic design of most modern air-conditioning systems utilizes four main components: an evaporator coil, a condenser coil, a compressor, and an expansion device.  Air inside the building is passed through the evaporator coil, which absorbs heat from the air (cools the air).  The compressor and expansion device circulate the refrigerant and modulate the refrigerant pressures inside the system.  The condenser coil is part of the outdoor unit and rejects heat to the atmosphere.  This requires outdoor air passing through the coil, which is achieved by a fan on the condenser portion of the system. 

Coil designs vary by manufacturer and type of equipment, but a widely used design utilizes a series of vertical aluminum fins.  The refrigerant tubes pass horizontally through the fins, and air is circulated between the fins and around the tubes, removing heat from the refrigerant in the process.

Fig. 1: Close-up view of undamaged condenser coil

The photograph above shows a close-up view of the fins in a typical condenser coil design.  The tubes can be seen running horizontally through the view, and the aluminum fins run vertically.  The space between the fins is uniform, and allows air to pass on both sides of the fin.  Heat is transferred from the refrigerant, through the tube wall, to the fins, and then to the air passing over the fins. 

When large hailstones strike a condenser coil, the thin aluminum fins are easily bent and folded over.  This results in a reduction of airflow through the coil.  When large percentages of the fins are folded over, this can cause reductions of the cooling capacity of the unit and energy efficiency. 

What is Combing and How Can it Help?

Combing is a process of straightening of the fins of the condenser coil utilizing small plastic combs that are sized to fit the spacing of the coils.  A comb can be run through the fins, restoring the gap and airflow between the fins.  In severe cases, pre-straightening techniques can be applied using plastic knives to open the fins prior to using the comb. 

Amset completed testing in-house to attempt to determine what extent of hail damage can be successfully restored using pre-straightening and combing techniques.  Figure two below shows severe damage to a coil that was simulated by throwing a golf ball against the coil at a high velocity.  As can be seen in the figure, the fins are folded completely flat in the center of these areas and in some cases, the fins are folded back against themselves like an accordion.

 Fig. 2: Close-up view of coil with simulated hail damage

Following the simulated damage, we applied various pre-straightening techniques, utilizing plastic knives and needle-nose pliers to re-open the gaps between the fins.  Figure three below shows the start of this process.

Fig. 3: Pre-straightening of coil

Once space is restored between each of the fins, the comb is used over several passes to complete the straightening process and restore a relatively even spacing between the fins.  Figure four below shows the start of the combing process.

Fig. 4: Combing of coil after pre-straightening

 Fig. 5: Coil after combing

Figure 5 above shows the area of the coil after the pre-straightening and combing was completed.  Some slight waviness can still be seen in the coil, but the spacing between the fins has been restored, thus restoring the airflow and capacity of the unit.  This shows that even very severe impacts to the coils can be restored if the coil is in otherwise good condition.  In some instances, the condition of the coil is such that the fins have become brittle over the years and may crack or rip during straightening.  In those cases, combing may not be possible.

How Can This Save on the Costs of the Claim?

When condenser coils have been hail damaged, the options are:  replace the entire outdoor unit, replace the coil, or comb the coil.  Combing is generally the most cost effective, but is labor intensive.  In years past, it was found in many cases of severe hail damage to be economical to replace the coil.  Due to the phaseout of R-22 refrigerant, many repairs of R-22 based equipment have become cost prohibitive.  The cost of R-22 refrigerant gas has skyrocketed in recent years, and repair parts for R-22 systems are becoming harder to find. 

Combing can restore the airflow and capacity of the coil without needing to open the system and incur any costs for parts or refrigerant.  In most cases, the repair does not restore the original look of the coil, but it can return the airflow and cooling capacity to pre-loss condition.  In cases where previous hail damage or other mechanical damage existed to the coil, the result after combing is actually better than pre-loss condition. 

 Fig. 6: Test combed section of actual hail damaged condenser

Figure six shows a hail damaged condenser with a test-combed section.  The hail damage to this unit was severe, and many contractors would state that it is not possible or feasible to comb this damage.  However, this test combed section has verified that it is indeed possible, and it was shown to be cost effective in this case.  In actual cases investigated by Amset, it has been shown that combing can provide a cost savings as high as 95% off of the claimed costs for replacement of the units. 

I hope you found this information helpful, and if you ever find yourself in need of a forensic engineering expert to assist you in streamlining the evaluation of your HVAC hail damage claims, contact Amset Technical Consulting and find out how we can help.

About the author:

Eric Dempsey, PE, CFEI, CVFI
Sr. Technical Loss Consultant

Eric Dempsey holds a Bachelor of Science degree in Mechanical Engineering from Iowa State University, and has been with Amset since 2007. Eric has prior experience with designing stainless steel storage tanks and ASME code pressure vessels for a custom tank manufacturer. Eric has extensive knowledge in manufacturing, cost-benefit analysis, investigative procedures, piping systems, and more. Eric’s natural inquisitiveness and hands-on approach to problem solving give him the ability to diagnose a wide variety of problems with all types of mechanical and electrical equipment. His unique approach to disseminating the facts has saved his clients both time and money on countless claims.

Eric is a Certified Fire and Explosion Investigator (CFEI) and a Certified Vehicle Fire Investigator (CVFI) through the National Association of Fire Investigators (NAFI). Eric’s professional memberships include the National Association of Fire Investigators (NAFI) and the Illinois Society of Professional Engineers (ISPE).